The present invention relates to pressure transmitters of the type used to measure pressure of a process fluid. More specifically, the invention relates to a coupling used to connect the pressure transmitter to a process fluid.
Transmitters are used to monitor the condition of industrial processes by measuring process variables such as pressure, temperature and flow. Pressure transmitters measure the pressure of a process fluid (gas or liquid) and transmit data related to the measured pressure to a remote control room over a process control loop.
There are two general types of pressure transmitters. Differential pressure transmitters measure the pressure differential between two process pressures and require two connections to the process fluid. The second type of pressure transmitter measures an absolute (relative or vacuum) or gage (relative to ambient pressure) pressure of the process fluid and requires a single coupling to the process fluid.
Some absolute or gage pressure transmitters have an in-line configuration in which a single pressure sensor, isolation diaphragm and process coupling are placed in an in-line configuration. Traditionally, in-line gage and absolute pressure transmitters have coupled to the process fluid using a threaded coupling. The threaded coupling of the transmitter is screwed onto a threaded pipe having a standardized configuration. The pipe couples to the process, for example, to process piping.
The threaded connections used to couple absolute or pressure gage pressure transmitters to process equipment can be a source of process leaks.
An in-line pressure transmitter for sensing an absolute or gage process pressure of a process fluid couples to the process using a non-threaded connection. The transmitter includes a pressure sensor which senses the process pressure and transmitter circuitry which provides an output related to the sensed process pressure. A single isolation diaphragm assembly isolates the process fluid from the pressure sensor. A transmitter housing contains the pressure sensor, transmitter circuitry and isolation diaphragm assembly. An in-line process coupling is welded to the housing having a mounting member which includes a substantially flat mounting face and a bore generally aligned with the isolation diaphragm assembly.